A wide variety of materials is used to enhance physical properties of plastics by acting as fillers or reinforcements. Fillers may be active or inert. When inert, they are primarily extenders. However, with the addition of an active material or coating, inert fillers can become reinforcements.
The most widely used extender filler for plastics is calcium carbonate. This material has been coated with stearic acid and calcium stearate to improve rheological properties. Organic materials such as salts of alkylolamines and long chain polyaminoamides with high molecular weight acids have also been used as coatings.
Kaolin or clay is the second most commonly used extender pigment in plastics. Treating clays with silane, polyester, and metal hydroxide for surface modifications is known in the art.
Other silicates such as glass, asbestos, and wollastonite have been used as reinforcements. Among the silicas are sand, quartz, and diatomaceous earth. Quartz has been used with phenolic and epoxy resins for high performance, aerospace applications.
Silane coupling agents are used in various prior art, composite products. The hydrolysis product of the coupling agent provides a bond to the inorganic components, and maintains good adhesion to siliceous fillers and reinforcements, even under environmental attack.
The silane coupling agents have significant effects when used with a wide range of thermosetting and thermoplastic resins. For example, when unsaturated polyester with various mineral fillers is treated with silane coupling agent, the viscosity of the entire system is reduced and both dry and wet flexural strength are improved. The viscosity reductions are particularly significant for sheet molding compounds when polyester resins are filled with alumina trihydrate treated with silane coupling concentrates.
Epoxy- and amino-functional silane coupling agents provide a high level of reactivity with the matrix resin in filled epoxy resins. Although this system had relatively little effect on dry strengths, wet properties are improved more than 100% with the use of epoxy-functional silane, and improvement is also noted in electrical properties.
The present invention differs from the practices of the prior art described above. Applicants do not use a pre-formed filler or reinforcement such as calcium carbonate or a silicate like glass or clay. Instead, Applicants prepare an inorganic/organic composite in situ. Secondly, Applicants do not use silanes as surface coatings for pre-formed fillers or reinforcers. Instead, they use such materials as reactants to form linking groups and as precursors for an in situ-prepared silica network. The linking groups bond an organic polymer to the in situ prepared network. This approach produces materials with improved high temperature mechanical properties, particularly above the glass transition temperature (Tg) of the organic polymer.